The Waveform Characteristics and Classification of Intermediate-depth Earthquakes in Ryukyu Subduction Zone

2020 ◽  
Author(s):  
Yu-Jhen Lin ◽  
Tai-Lin Tseng ◽  
Wen-Tzong Liang
Keyword(s):  
Subduction Zone ◽  
High Frequency ◽  
Time Window ◽  
Source Region ◽  
Focal Depth ◽  
Low Frequency ◽  
Frequency Content ◽  
Low Velocity ◽  
Waveform Data ◽  
Intermediate Depth

<p>Using intraslab earthquakes shallower than 150 km in the southernmost Ryukyu subduction zone, previous studies in Taiwan found the wave guide effect that typically shows a low-frequency (<2Hz) first P arrival followed by sustained high-frequency (3–10 Hz) wave trains. Recently occurred deeper events at depth 150-300 km allow us to better quantify the properties of those seismic waves traveling in the subduction zone. In this study, we aim to systematically scan through the local broadband waveforms of the intermediate depth earthquakes with M>5 between 1997 and 2016. Event are classified based on the waveform characteristics and their frequency contents.</p><p>To detect events with similar properties, we applied sliding-window cross-correlation (SCC)​ using three components of P waveform data simultaneously for a set of stations​. The time window used here was 10 s and traces were bandpass filtered in the frequency range 0.5–10 Hz. After the degree of similarity are calculated, e​vents containing comparable waveforms can be sorted into families. The events within a family would have been triggered because they came from the same source region and their paths to a particular receiver should produce similar waveforms. Our results show that most earthquakes are low in waveform similarity, implying no “repeating” behavior for those intermediate intraslab events. However, some events (cc>0.6 threshold) present enough charterers that can be grouped as a family.</p><p>One important property is the frequency content of the arrivals that may be related to the speed of structure traveled. We have developed a work scheme to determine the delayed time of higher-frequency energy. On family of events show beautiful dispersion with arrival time smoothly increasing with frequency between 0.5 and 6 Hz.​ Another type of dispersive waveforms appear as two distinct arrivals: low frequency and then high-frequency energy, separated by around 1 s. The time delay seems to be independent of focal depth. The latter case has been reported in the previous study for shallower event and it was interpreted as effect from low-velocity layer or heterogeneity of the subducted slab. On the other hand, the continuous dispersion is a new feature observed by our study, which may infer a thinner layer and/or longer propagation for some kind of reflecting waves to develop such interference.</p><p>In addition, we will classify the waveforms according to the frequency content and decay of coda. The variations in P coda properties can be associated with the way in which the seismic energy gets ducted into the stochastic waveguide associated with the lithosphere. With sufficient amount of data, it is possible to further identify the earthquakes with unusual source properties or structure anomaly along specific propagation paths. We expect the classification results can provide a reference for future numerical simulation analysis. </p><p>Keywords: Ryukyu subduction zone, SCC, guide wave, waveform classification, intermediate-depth earthquakes</p>

Spatial distribution of high-frequency energy radiation on the fault of the 1995 Hyogo-Ken Nanbu, Japan, earthquake (MW 6.9) on the basis of the seismogram envelope inversion

1999 ◽  
Vol 89 (1) ◽  
pp. 22-35 ◽  
Author(s):  
Hisashi Nakahara ◽  
Haruo Sato ◽  
Masakazu Ohtake ◽  
Takeshi Nishimura
Keyword(s):  
Spatial Distribution ◽  
Wave Energy ◽  
High Frequency ◽  
Fault Plane ◽  
Time Window ◽  
Source Region ◽  
Inversion Method ◽  
S Wave ◽  
Energy Radiation ◽  
Initial Rupture

Abstract We studied the generation and propagation of high-frequency (above 1 Hz) S-wave energy from the 1995 Hyogo-Ken Nanbu (Kobe), Japan, earthquake (MW 6.9) by analyzing seismogram envelopes of the mainshock and aftershocks. We first investigated the propagation characteristics of high-frequency S-wave energy in the heterogeneous lithosphere around the source region. By applying the multiple lapse time window analysis method to aftershock records, we estimated two parameters that quantitatively characterize the heterogeneity of the medium: the total scattering coefficient and the intrinsic absorption of the medium for S waves. Observed envelopes of aftershocks were well reproduced by the envelope Green functions synthesized based on the radiative transfer theory with the obtained parameters. Next, we applied the envelope inversion method to 13 strong-motion records of the mainshock. We divided the mainshock fault plane of 49 × 21 km into 21 subfaults of 7 × 7 km square and estimated the spatial distribution of the high-frequency energy radiation on that plane. The average constant rupture velocity and the duration of energy radiation for each subfault were determined by grid searching to be 3.0 km/sec and 5.0 sec, respectively. Energy radiated from the whole fault plane was estimated as 4.9 × 1014 J for 1 to 2 Hz, 3.3 × 1014 J for 2 to 4 Hz, 1.5 × 1014 J for 4 to 8 Hz, 8.9 × 1012 J for 8 to 16 Hz, and 9.8 × 1014 J in all four frequency bands. We found that strong energy was mainly radiated from three regions on the mainshock fault plane: around the initial rupture point, near the surface at Awaji Island, and a shallow portion beneath Kobe. We interpret that energetic portions were associated with rupture acceleration, a fault surface break, and rupture termination, respectively.

Broadband seismic over/under sources and their designature-deghosting

Geophysics ◽  
2017 ◽  
Vol 82 (5) ◽  
pp. P61-P73 ◽  
Author(s):  
Lasse Amundsen ◽  
Ørjan Pedersen ◽  
Are Osen ◽  
Johan O. A. Robertsson ◽  
Martin Landrø
Keyword(s):  
Seismic Data ◽  
High Frequency ◽  
Low Frequency ◽  
Point Sources ◽  
High Frequency Side ◽  
Frequency Content ◽  
Source Depth ◽  
Deep Sources ◽  
The Cost ◽  
High Frequency Content

The source depth influences the frequency band of seismic data. Due to the source ghost effect, it is advantageous to deploy sources deep to enhance the low-frequency content of seismic data. But, for a given source volume, the bubble period decreases with the source depth, thereby degrading the low-frequency content. At the same time, deep sources reduce the seismic bandwidth. Deploying sources at shallower depths has the opposite effects. A shallow source provides improved high-frequency content at the cost of degraded low-frequency content due to the ghosting effect, whereas the bubble period increases with a lesser source depth, thereby slightly improving the low-frequency content. A solution to the challenge of extending the bandwidth on the low- and high-frequency side is to deploy over/under sources, in which sources are towed at two depths. We have developed a mathematical ghost model for over/under point sources fired in sequential and simultaneous modes, and we have found an inverse model, which on common receiver gathers can jointly perform designature and deghosting of the over/under source measurements. We relate the model for simultaneous mode shooting to recent work on general multidepth level array sources, with previous known solutions. Two numerical examples related to over/under sequential shooting develop the main principles and the viability of the method.

scholarly journals Towards improving the physical basis for ice-dynamics models

1997 ◽  
Vol 25 ◽  
pp. 177-182 ◽  
Author(s):  
J. A. Richter-Menge
Keyword(s):  
High Frequency ◽  
Low Frequency ◽  
The Arctic ◽  
Frequency Content ◽  
Ice Dynamics ◽  
Relative Significance ◽  
Thermally Induced ◽  
Induced Stress ◽  
Dynamics Models

In situ measurements of ice stress were made on a multi-year floe in the Alaskan Beaufort Sea over a 6 month period, beginning in October 1993. The data suggest that, in this region of the Arctic during this experiment, there were two main sources of stress: a thermally induced stress caused by changes in air temperature, and a stress generated by ice motion. Due to the natural damping of the snow and ice above the sensor, the thermally-induced stresses are low frequency (order of days). Stresses associated with periods of ice motion have both a high-frequency (order of hours), and low-frequency, content. The relative significance of these sources of stress is seasonal, reflecting the changes in the strength and continuity of the pack.

scholarly journals A LSTM-STW and GS-LM Fusion Method for Lithium-Ion Battery RUL Prediction Based on EEMD

Energies ◽  
2020 ◽  
Vol 13 (9) ◽  
pp. 2380 ◽  
Author(s):  
Ling Mao ◽  
Jie Xu ◽  
Jiajun Chen ◽  
Jinbin Zhao ◽  
Yuebao Wu ◽  
...  
Keyword(s):  
Lithium Ion Battery ◽  
High Frequency ◽  
Short Term Memory ◽  
Time Window ◽  
Low Frequency ◽  
Lithium Ion ◽  
Remaining Useful Life ◽  
Marquardt Algorithm ◽  
Starting Point ◽  
Frequency Components

To address inaccurate prediction in remaining useful life (RUL) in current Lithium-ion batteries, this paper develops a Long Short-Term Memory Network, Sliding Time Window (LSTM-STW) and Gaussian or Sine function, Levenberg-Marquardt algorithm (GS-LM) fusion batteries RUL prediction method based on ensemble empirical mode decomposition (EEMD). Firstly, EEMD is used to decompose the original data into high-frequency and low-frequency components. Secondly, LSTM-STW and GS-LM are used to predict the high-frequency and low-frequency components, respectively. Finally, the LSTM-STW and GS-LM prediction results are effectively integrated in order to obtain the final prediction of the lithium-ion battery RUL results. This article takes the lithium-ion battery data published by NASA as input. The experimental results show that the method has higher accuracy, including the phenomenon of sudden capacity increase, and is less affected by the prediction starting point. The performance of the proposed method is better than other typical battery RUL prediction methods.

scholarly journals Simultaneous rupture on conjugate faults during the 2018 Anchorage, Alaska, intraslab earthquake (MW 7.1) inverted from strong-motion waveforms

2020 ◽  
Author(s):  
Yujia Guo ◽  
Ken Miyakoshi ◽  
Masato Tsurugi
Keyword(s):  
Subduction Zone ◽  
Source Parameters ◽  
Source Region ◽  
Rare Event ◽  
Strong Motion ◽  
Great Depth ◽  
North American Plate ◽  
Low Velocity ◽  
Intraslab Earthquake ◽  
Simultaneous Rupture

Abstract An MW 7.1 ~50-km-deep intraslab earthquake within the Pacific/Yakutat slab underlying the North American Plate struck Anchorage, southern Alaska, on November 30, 2018. The ground-motion records very close to the source region of the Anchorage earthquake provide an important opportunity to better understand the source characteristics of intraslab earthquakes in this subduction zone. We estimated the kinematic rupture process during this earthquake using a series of strong-motion waveform (0.05–0.4 Hz) inversions. Our inversions clearly indicate that the Anchorage earthquake was a rare intraslab event with simultaneous rupture on two conjugate faults, which are recognized sometimes for shallow crustal earthquakes but rarely for deep intraslab earthquakes. Interestingly, one of the conjugate faults had low aftershock productivity. This fault extends to great depth and may reflect a deep oceanic Moho or a local low-velocity and high-VP/VS zone within the oceanic mantle. Even though the Anchorage earthquake was a rare event due to the conjugate faults, we found that its kinematic source parameters such as the slip amplitude and large-slip area nearly equal the global averages derived from source scaling relationships for intraslab earthquakes. Because the source parameters comparable to the global averages were also found for another large intraslab earthquake in the subducting Pacific/Yakutat slab, these source parameters are likely an important source characteristic common to this subduction zone.

scholarly journals The nature of the extreme X-ray variability in the NLS1 1H 0707-495

2021 ◽  
Author(s):  
M L Parker ◽  
W N Alston ◽  
L Härer ◽  
Z Igo ◽  
A Joyce ◽  
...  
Keyword(s):  
High Frequency ◽  
Low Frequency ◽  
Emission Lines ◽  
Intrinsic Variability ◽  
Low Velocity ◽  
Strong Suppression ◽  
X Ray ◽  
Low Frequency Variability ◽  
High Frequency Variability ◽  
Long Timescales

Abstract We examine archival XMM-Newton data on the extremely variable narrow-line Seyfert 1 (NLS1) active galactic nucleus (AGN) 1H 0707-495. We construct fractional excess variance (Fvar) spectra for each epoch, including the recent 2019 observation taken simultaneously with eROSITA. We explore both intrinsic and environmental absorption origins for the variability in different epochs, and examine the effect of the photoionised emission lines from outflowing gas. In particular, we show that the unusual soft variability first detected by eROSITA in 2019 is due to a combination of an obscuration event and strong suppression of the variance at 1 keV by photoionised emission, which makes the variance below 1 keV appear more extreme. We also examine the variability on long timescales, between observations, and find that it is well described by a combination of intrinsic variability and absorption variability. We suggest that the typical extreme high frequency variability which 1H 0707-495 is known for is intrinsic to the source, but the large amplitude, low frequency variability that causes prolonged low-flux intervals is likely dominated by variable low-ionisation, low velocity absorption.

High-frequency radiation process during earthquake faulting—envelope inversion of acceleration seismograms from the 1993 Hokkaido-Nansei-Oki, Japan, earthquake

1997 ◽  
Vol 87 (4) ◽  
pp. 904-917 ◽  
Author(s):  
Yasumaro Kakehi ◽  
Kojiro Irikura
Keyword(s):  
High Frequency ◽  
Fault Plane ◽  
Source Region ◽  
Low Frequency ◽  
Strong Motion ◽  
Rupture Process ◽  
Wave Radiation ◽  
Radiation Process ◽  
Frequency Wave ◽  
High Frequency Wave

Abstract We investigate the process of high-frequency (1 to 10 Hz) radiation on the fault plane of the 1993 Hokkaido-Nansei-Oki, Japan, earthquake (MW = 7.5) from the envelope inversion of strong-motion acceleration seismograms. For the analysis, empirical Green's functions are used because theoretical approach is not available for such high frequencies. The source is modeled with two fault planes with different strike angles. The rupture process of this earthquake is very complex in terms of high-frequency wave generation. The rupture, which started on the northern fault plane, had a delay of about 10 sec or propagated very slowly between the northern and southern fault planes. High-frequency wave radiation is large at the northern and southern edges of the source region. Deceleration of rupture is also observed there. This is interpreted to be associated with stopping of rupture. Another high-frequency wave radiation area is found at the center of the northern fault plane, where discontinuity in the depth distribution of aftershocks suggests an existence of a barrier. The areas of high- and low-frequency wave radiation are not correlated. This is considered to result from the complexity of rupture process. We cannot distinguish between westward and eastward dip of the southern fault plane because of one-sided station distribution.

Frequency Effects on Spelling Error Recognition: An ERP Study

2022 ◽  
Author(s):  
Ekaterina Larionova ◽  
Olga Martynova
Keyword(s):  
Word Frequency ◽  
High Frequency ◽  
Word Processing ◽  
Time Course ◽  
Time Window ◽  
Low Frequency ◽  
Spelling Error ◽  
Spelling Errors ◽  
Error Recognition ◽  
High Frequency Words

Spelling errors are ubiquitous in all writing systems. Most studies exploring spelling errors focused on the phonological plausibility of errors. However, unlike typical pseudohomophones, spelling errors occur in naturally produced written language with variable frequencies. We investigated the time course of recognition of the most frequent orthographic errors in Russian (error in an unstressed vowel at the root) and the effect of word frequency on this process. During ERP recording, 26 native Russian speakers silently read high-frequency correctly spelled words, low-frequency correctly spelled words, high-frequency words with errors, and low-frequency words with errors. The amplitude of P200 was more positive for correctly spelled words than for misspelled words and did not depend on the frequency of the words. Word frequency affected spelling recognition in the later stages of word processing (350-700 ms): high-frequency misspelled words elicited a greater P300 than high-frequency correctly spelled words, and low-frequency misspelled words elicited a greater N400 than low-frequency correctly spelled words. We observe spelling effects in the same time window for both the P300 and N400, which may reflect temporal overlap between mainly categorization processes based on orthographic properties for high-frequency words and phonological processes for low-frequency words. We concluded that two independent pathways can be active simultaneously during spelling recognition: one reflects mainly orthographic processing of high-frequency words and the other is the phonological processing of low-frequency words. Our findings suggest that these pathways are associated with different ERP components. Therefore, our results complement existing reading models and demonstrate that the neuronal underpinnings of spelling error recognition during reading depend on word frequency.

scholarly journals Simultaneous rupture on conjugate faults during the 2018 Anchorage, Alaska, intraslab earthquake (MW 7.1) inverted from strong-motion waveforms

2020 ◽  
Vol 72 (1) ◽  
Author(s):  
Yujia Guo ◽  
Ken Miyakoshi ◽  
Masato Tsurugi
Keyword(s):  
Subduction Zone ◽  
Source Parameters ◽  
Source Region ◽  
Rare Event ◽  
Strong Motion ◽  
Great Depth ◽  
North American Plate ◽  
Low Velocity ◽  
Intraslab Earthquake ◽  
Simultaneous Rupture

AbstractAn MW 7.1 ~ 50-km-deep intraslab earthquake within the Pacific/Yakutat slab underlying the North American Plate struck Anchorage, southern Alaska, on November 30, 2018. The ground-motion records very close to the source region of the Anchorage earthquake provide an important opportunity to better understand the source characteristics of intraslab earthquakes in this subduction zone. We estimated the kinematic rupture process during this earthquake using a series of strong-motion waveform (0.05–0.4 Hz) inversions. Our inversions clearly indicate that the Anchorage earthquake was a rare intraslab event with simultaneous rupture on two conjugate faults, which are recognized sometimes for shallow crustal earthquakes but rarely for deep intraslab earthquakes. Interestingly, one of the conjugate faults had low aftershock productivity. This fault extends to great depth and may reflect a deep oceanic Moho or a local low-velocity and high-VP/VS zone within the oceanic mantle. Even though the Anchorage earthquake was a rare event due to the conjugate faults, we found that its kinematic source parameters such as the slip amplitude and large slip area nearly equal the global averages derived from source scaling relationships for intraslab earthquakes. Because the source parameters comparable to the global averages were also found for another large intraslab earthquake in the subducting Pacific/Yakutat slab, these source parameters are likely an important source characteristic common to this subduction zone.

scholarly journals Simulation of Broadband Ground Motion by Superposing High-Frequency Empirical Green’s Function Synthetics on Low-Frequency Spectral-Element Synthetics

Geosciences ◽  
2020 ◽  
Vol 10 (9) ◽  
pp. 339
Author(s):  
Ramses Mourhatch ◽  
Swaminathan Krishnan
Keyword(s):  
Ground Motion ◽  
Green's Function ◽  
Seismic Wave ◽  
High Frequency ◽  
Low Frequency ◽  
Spectral Element ◽  
Time Shift ◽  
Frequency Content ◽  
Empirical Green's Function ◽  
High Frequency Content

Seismic wave-propagation simulations are limited in their frequency content by two main factors: (1) the resolution of the seismic wave-speed structure of the region in which the seismic waves are propagated through; and (2) the extent of our understanding of the rupture process, mainly on the short length scales. For this reason, high-frequency content in the ground motion must be simulated through other means. Toward this end, we adopt a variant of the classical empirical Green’s function (EGF) approach of summing, with suitable time shift, recorded seismograms from small earthquakes in the past to generate high-frequency seismograms (0.5–5.0 Hz) for engineering applications. We superimpose these seismograms on low-frequency seismograms, computed from kinematic source models using the spectral element method, to produce broadband seismograms. The non-uniform time- shift scheme used in this work alleviates the over-estimation of high-frequency content of the ground motions observed. We validate the methodology by simulating broadband motions from the 1999 Hector Mine and the 2006 Parkfield earthquakes and comparing them against recorded seismograms.

Sign in / Sign up

Export Citation Format

Share Document